Dystroglycan (DG) is a conserved cell surface receptor that serves to link extracellular basement membrane and intracellular cytoskeletal and signaling components. DG has been extensively studied in muscle cells where it links laminin to dystrophin, as part of the complex that is disrupted in muscular dystrophies. Dystrophies associated with brain abnormalities, such as Fukuyama muscular dystrophy, result from defects of DG processing and reveal its importance in neural and epithelial cells. The specific functions of DG in non-muscle cells, however, are poorly understood. We have shown that the C. elegans DG ortholog, DGN-1, has critical functions in many neural/epithelial cells, but is not required in muscle. DGN-1 mutant defects include abnormal cell adhesion and migration, aberrant axon guidance and defective synaptic transmission. Thus, in vivo studies using the powerful genetic tools available in C. elegans may clarify how DG functions in neurons and epithelia. DG functions are highly cell type dependent, and we hypothesize that specific extracellular and intracellular factors are critical in determining the physiological roles of DG in different contexts. Using transgenic analysis of altered DGN-1 constructs expressed in DGN-1 null animals, we will determine which domains of DGN-1 are involved in the particular neural/epithelial functions we have described. The importance of particular extracellular ligands will be analyzed by transgenic expression of dominantly interfering ligand domains and/or complete replacement of ligand molecules with specifically altered versions. Intracellular ligands will be identified using yeast two-hybrid technology and RNAi knockdown of candidates. Genetic screens will be pursued to generate novel DGN-1 mutations that will define important aspects of DG structure, and extragenic enhancers or suppressors of DGN-1 function, that can identify interacting molecules. Also, we have shown that transgenic expression of altered DGN-1 can dominantly induce neural/epithelial phenotypes, and genetic screens to suppress these effects will be used to identify upstream and/or downstream effectors of DGN-1 function. This combination of targeted and random genetic approaches will provide in vivo evidence for particular extracellular and intracellular ligand interactions underlying specific DG functions in specific cells.